This invention relates to a process for making rare earth oxysulfide phosphors resistant to hydrolysis and to the hydrolysis resistant phosphors thus produced. More particularly it relates to a process for making rare earth oxysulfide phosphors resistant to hydrolysis by imparting a silicate coating thereon, and to the silicate coated hydrolysis resistant phosphor thus produced.
Rare earth oxysulfide phosphors have become successful x-ray intensifier phosphors. In this application the phosphor is on a screen called an intensifier screen. The screen is mounted in a cassette where in operation the phosphor thereon is exposed to x-rays. The phosphor converts the x-rays into visible or near visible radiation to which a photosensitive film is exposed resulting in an image being produced on the film.
One of the problems that has developed in the above application is that if the phosphor comes in contact with water, a hydrolytic reaction can occur and hydrogen sulfide is released. Additionally, if water is inadvertently dropped on an intensifying screen in an x-ray cassette and a film is placed in the cassette, a reaction between hydrogen sulfide and the silver halide in the film emulsion occurs. This reaction causes a brown stain on the intensifying screen that reduces the speed of the screen resulting in inferior radiographs.
Therefore, if the phosphors could be made resistant to hydrolysis so that they consistently produce good radiographs, it would be highly desirable and an advancement in the art.